The technical field of this invention is object surface characterization using optical triangulation ranging.
When cameras are used for optical triangulation ranging, the most common approach requires a stereo vision system. Besides the cost and speed disadvantages, the distance measurement accuracy of the system is typically poor when the object lacks surface texture. In some alternative approaches, temporally encoded probing beams can be used with a single camera for triangulation. In those systems, the probing beams are sequentially directed to different parts of the object through beam scanning or control of light source arrays. But such methods are either not suitable for high volume production or they are limited in spatial resolution. Because the distance is measured one point at a time, fast two dimensional (2D) ranging cannot be achieved unless an expensive high-speed camera is used.
The real challenge of using a single camera with simultaneously projected probing beams for triangulation is to efficiently distinguish each individual beam image from the rest of the beam images on the image plane. The target distance is measured through the correlation between the distance of the target upon which the beam is projected and the location of the returned beam image on the image plane. Such a correlation is different for each beam. When multiple beam images are simultaneously projected, one particular location on the image plane may be correlated with several beam images with different target distances. In order to measure the distance correctly, each beam image must be labelled without ambiguity.
Electromagnetic radiation is directed from an optical grating in a regular array of beams in rows and columns toward a target object surface; and the reflected beams are focused through a lens to form beam images on an image plane of a single camera. Each of the beam images has a position on the image plane that moves substantially linearly with variation of a target distance between the optical grating and a point on the object surface from which that beam image is reflected; and the direction of the substantially linear movement of each beam image forms a predetermined angle with the column of the array of beam images on the image plane to which that beam belongs at a common target distance. Positional data for each of the beam images on the image plane is derived and provided to a processor which uses stored reference data defining predetermined beam paths in the image plane for the beam images to locate and determine the associated one of the predetermined beam paths for each of the beam images on the image plane, determine the location of each of the beam images along its associated predetermined beam path, determine the target distance for that beam and store an array of the determined target distances for each of the located beam images to characterize the object surface. The predetermined angle may provide for each beam having a separate predetermined beam path. For greater resolution, some of the beam paths may have two associated beams, and processing is provided to distinguish the beams on a single beam path uniquely.
For embodiments in which some predetermined beam paths are associated with pairs of beam images, the beam images can be uniquely identified by the presence of only one of the beam images in a range of locations defined by a region cutoff datum in which only that beam may be found and the location of the other of the pair of beam images outside the region. If neither of the pair of beam images is located in the range of locations, the beam images may be uniquely identified by examining their locations relative to those of other uniquely identified beam images in other beam paths.